It is well established that HTLV-I is the etiologic agent for a number of diseases, including adult T-cell leukemia and a neurological disorder called HAM/TSP. In addition, accumulating evidence suggests that HTLV-II may be involved in disease, as well. These disease correlations, and the fact that HTLV-I and HTLV-II can be transmitted by transfusion, have led to the recommendation that blood donors be screened for evidence of HTLV-I and HTLV-II infection. However, the connection between the virus and disease is not known. The purpose of this project is to examine molecular mechanisms which could explain such a connection, thereby establishing a basis for HTLV-associated transfusion-transmitted disease. In addition, this project seeks to determine if current methods for screening blood donors are sufficient to detect both HTLV-I and HTLV-II infections. In the area of detection and blood safety, we coordinated a response to reports that HTLV-I Tax sequences could be detected in up to 11% of normal healthy random blood donors who were negative on conventional HTLV-I/HTLV-II screening tests. This response was designed to determine the reproducibility of those reports. Laboratories from FDA, CDC, the Retrovirus Epidemiology Donor Study, and New York University analyzed specimens collected from 100 HTLV-I/II seronegative healthy random donors and from 11 individuals known to be infected with HTLV-I or HTLV-II. All test sites were blinded to the identity of each specimen, and methods of sample preparation and analysis by PCR were identical to those used by the laboratory at New York University which made the original observations. The results demonstrated that HTLV Tax sequences could not be detected reproducibly in any of the HTLV-I/II seronegative healthy random donors, and indicated that current donor screening tests are effective at preventing the transfusion transmission of HTLV-I and HTLV-II. In the area of HTLV-I-associated neurological disease, we continued studies on the effects of purified HTLV-I Tax protein on gene expression in NT2-N, post-mitotic cells that are remarkably similar to primary human neurons. In the past, we observed that treatment of NT2-N with soluble Tax resulted in the synthesis of TNF-alpha in a dose-dependent manner and that exposing NT2-N to Tax for as little as 5 minutes was sufficient to result in TNF-alpha production. Thus, the induction of TNF-alpha in NT2-N does not require Tax to be continually present. We have since demonstrated that TNF-alpha itself is sufficient to induce TNF-alpha production in NT2-N. Therefore, the role of Tax may simply be to induce an initial burst of TNF-alpha synthesis, which will then sustain continued production of TNF-alpha. Given the toxicity of TNF-alpha for oligodendrocytes, the myelin-producing cells of the central nervous system, these results suggest that extracellular Tax may play a role in the demyelination observed in HAM/TSP through the induction of TNF-alpha in neurons. An animal model is being developed to test this hypothesis. In addition, samples of cerebrospinal fluid and blood from HTLV-I-infected individuals with and without disease are being examined for the presence of Tax protein in an effort to correlate the presence of Tax with disease.